Process of converting copper



Patented July 11, 1939 UNITED STATES PATENT OFFIQE PROCESS OF CONVERTING COPPER SULPHIDE No Drawing Application January 4, 1937, Serial No. 118,994

8 Claims.

The present invention relates to the production of copper hydroxide, and more particularly to the conversion of copper sulphide into copper hydroxide.

The main object of the invention is to cheapen the recovery of copper in the form of copper hydroxide or basic copper salts from the Waste liquors resulting from the manufacture of rayon by the cupro-ammonium process.

In the manufacture of rayon according to the cupro-ammonium process, the quantities of copper hydroxide required for dissolving or digesting the cellulose amount to from 50 to 65 per cent of the weight of the cellulose. In order to render this process more fully competitive with other methods of rayon manufacture, it is important not only that as much as possible of the copper hydroxide is reclaimed and returned to use, but also that its recovery is carried out in the cheapest possible manner.

In the process, as described in U. S. P. #1,770,'750 in which 4% solution of cellulose is precipitated by caustic soda, a substantial part of the copper contained in the spinning solution (20%) is dissolved by the caustic soda liquor, the remaining 80 to 85 per cent is recovered in the form of a dilute copper sulphate solution containing a little free sulphuric acid.

In order to recondition the precipitating solution for repeated use, which is also an economical exigency of the process, said part is removed therefrom by adding an equivalent amount of a suitable sulphide and by eliminating the re sultant insoluble precipitate of copper sulphide by filtration or decantation.

In this manner, the copper absorbed by the precipitating bath is made available for recovery in the form of copper sulphide.

To convert it into purified copper hydroxide or basic copper sulphate fit for preparing cellulose solutions, the usual proceedings consist in first freeing the copper sulphide from adhering caustic by washing, in then digesting it to copper sulphate with the necessary amount of sulphuric acid in the presence of an oxidizing agent, such as chlorates, peroxides, etc. and in further treating the resultant solution in known manner to form purified copper hydroxide as for example according to the method outlined by U. S. Patents #l,800,828 and #1367357.

Now, I have found that copper sulphide can, in one operation, be converted into copper hydroxide, if it is subjected to oxidizing action in the presence of caustic or other alkalis, and that, under such conditions, its tendency for oxidation becomes so strong, that the desired conversion can be quickly and completely effected by air oxidation.

In carrying out this process, the copper sulphide suspended in dilute caustic soda solution is aerated and agitated to efiect contact of air with the suspension.

The quantity of caustic soda present should be in excess of that required for forming a thiosulphate salt with the known sulphur content of the precipitate. If it is lower, it becomes increasingly difiicult to carry the reaction to its completion.

While the present invention is capable of general application, conditions for its use in an alkaline precipitation of cuprammonium cellulose solutions-as for instance in U. S. Patent #l,'770,750are exceptionally favorable: Since, in this case, the copper sulphide, as it is removed from the withdrawn precipitating liquor, is alkaline, the washing operation is omitted and no extra caustic added for conversion into copper hydroxide. Moreover, not only the copper value, but also the acid-neutralizing power of the resulting copper hydroxide can be utilized by dissolving it in the waste acid liquor which contains the balance of the copper content of the spinning solution in the form of copper sulphate, in addition to a certain percentage of free acid which has to be neutralized for recovering the copper. In order to recover the copper of the acid waste solution, it is necessary to neutralize the free sulphuric acid contained therein. By utilizing for this purpose the above mentioned copper hydroxide obtained from the conversion of the copper sulphide, considerable economy results as we can dispense with the corresponding amount of caustic soda which would otherwise be necessary for such neutralization.

If we assume that when using caustic soda as the alkali the conversion of copper sulphide as above described takes place in accordance with the formula the acid neutralizing power of the copper hydroxide formed in the reaction is twice as great as that of the caustic soda utilized in the reaction that produces the copper hydroxide.

A study of the equation given above will clarify this point. The active principle here involved in acid neutralizing value is the presence of hydroxyl (OH) groups. On the left hand side of the reaction we have two such groups, namely in the ZNaO-H. On the right hand side We have four, in the 2Cu(OH)2. The extra two OH groups are formed from one molecule of H20 and one of the oxygen atoms on the left hand side. The acid neutralizing power of the products on the left and right hand sides of the equation may be shown as follows:

Thus it is seen that the acid neutralizing power of the copper hydroxide formed in the reaction is twice as great as that of the caustic soda used to produce the copper hydroxide. Thus I have not only developed a novel and economical meth d of converting copper sulphide into a compound easily soluble in dilute acid, but have actually manufactured alkali from water and oxygen of the air.

It should be noted that copper sulphide itself has no acid-neutralizing value in the sense in which we are here concerned, i. e. the power of dissolving in a dilute acid, such as sulphuric acid. It can only be dissolved in a strong oxidizing acid, such as nitric -cid or aqua regla, or by fairly strong sulphuric acid in combination with an oxidizing agent such as chlorates, peroxides, etc. Heating is also necessary.

Only about 15 to 20% of the copper is recovered from the alkaline setting bath in the form of copper sulphide. The remainder is obtained in the form of a weak solution of copper sulphate containing a little free sulphuric acid (about 0.1 to 0.2%). This free acid, while small in concentration, is large in aggregate, because large volumes are involved, and it all has to be neutralized by alkali in the recovery of copper by the c sulphate method. The copper hyeonverted from copper sulphide by the process dissolves readily in acid waste the above dilution, thereby utilizing not liquor of only its copper value, but also its acid neutralizing power.

Contrasting with the, the former use involved digesting the copper sulphide in a hot and fairly strong solution of sulphuri acid nethod in in the presence of an oxidizing agent. In the present process, not only do We eliminate the oxidizing agent and all the extra acid, but we obtain from the copper hydroxide produced a considerable part of the alkali value needed to neutralize the i'ree acid in the main copper solution. Thereiore the acid neutralizing feature dovetails into the process of copper recovery and should be considered as part of an economic whole.

in practice, the precipitate of copper sulphide is not pure cupric sulphide, but contains a considerable portion of cuprous sulphide. This further lowers the consumption of caustic soda in accordance with the following reaction:

it also involves substantial savings in that direction as well as in labor and installation.

Other alkalies may be used in place of caustic soda as for instance potassium hydroxide, alkaline carbonates such as sodium carbonate may also be used although the reaction in the latter case is slower.

The same process may be applied to copper sulphide ore. For this purpose the ore should be very finely powdered. The treatment is carried out as described above using aeration in the presence of caustic soda solution whereupon the copper sulphide is transformed into copper hydroxide.

Example #1 To 1,000 lbs. of a press-cake derived from a caustic soda precipitating bath and containing about 190 lbs. of precipitated copper sulphide, the remainder by weight being substantially all water in which a little caustic soda, about 3.5%, remains from the precipitating bath, 3,600 litres water are introduced into an iron tank and the copper sulphide kept suspended by agitation.

180 lbs. of caustic (50%) are added. The contents of the tank are then aerated as by agitating with a type of agitator that beats air into the solution, e. g. the so-cailed aerator agitator. The conversion is completed when a sample is cornpletely soluble in dilute sulphuric acid which point should be reached within 6-3 'iGlll'S. The time will vary with the speed or" aeration. As the amount of caustic soda present should be in excess of that required for forming a thiosulphate salt with the known sulphur content of the precipitate, more caustic may be added before aerating the mixture should the caustic soda content of the filter-cake be below that mentioned above.

The resultant copper hydroxide is washed by decantation.

Example #2 In the manufacture of synthetic fibres, according to the cuprammoniurn method, withdrawn alkaline precipitating liquor has to be reconditioned for circulation. One of the treatments necessary for this purpose consists in removing the gain in copper by adding equivalent amount of sodium sulphide and by th n leading the liquid through various settling tanks where the insoluble copper sulphide accumulates on the bottom and istherefrom periodically withdrawn for recovery.

4,000 litres of the withdrawn sediment containing 275 lbs. of copper sulphide and about 121 lbs. of caustic soda are drawn into a tank and are brought to about 6,000 litres by adding water. The contents are then stirred with an aerator agitator until a sample is substantially completely soluble in dilute sulphuric acid.

The resulting copper hydroxide is washed with water and may be further pu "ified in any known or other suitable manner.

My invention is susceptible to modification as is always the case. All modifications partaking of the generic spirit of the invention should unuestionably be protected to me.

Moreover, the relative purity of the substances used and the relative purity of the compounds produced does not occasion departure from the spirit of my invention. Thus for example, the copper hydroxide which is produced may be 100% pure copper hydroxide or it may be a partially dehydrated copper hydroxide, a pure copper hydroxide admixed with copper oxide in complete or stage formation. Thus the natiu'al bright blue color of the pure copper hydroxide may be tinged brown or black.

Thus in the second instance where washing may ordinarily be omitted in the instance of utilization of waste precipitating liquor possessed of proper alkalinity to begin with, in those cases where the alkalinity is in excess of that, needful Washing may be resorted to to bring the alkalinity to the value desired. Neither these nor any other such variations in quality of substances or compounds detract from the generic spirit of the invention. The important thing is that the copper hydroxide product which is claimed shall be usable for the purposes specified, and this I found to be true irrespective of the number of such variations in detail.

What I claim is:

1. A process of converting copper sulphide into copper hydroxide which consists in suspending the copper sulphide in an alkaline solution of a metallic base, and agitating that solution and permeating it with air during agitation thereby yielding copper hydroxide free of acid ions.

A process of converting copper sulphide into copper hydroxide which consists in suspending the copper sulphide in an alkaline solution of a metallic base, and agitating that solu tion and permeating it with air during the agitation, said alkali being caustic soda thereby yielding copper hydroxide free of acid ions.

3. A process of converting copper sulphide into copper hydroxide which consists in suspending the copper sulphide in an alkaline solution of a metallic base, and agitating that solution and permeating it with air during the agitation, said alkaline solution having a concentration in excess of that required for forming a thiosulphate salt with the known sulphur content of the precipitate thereby yielding copper by droxide free of acid ions.

4. In a process for recovering copper content from the precipitating liquor of the cuproammonium process of rayon manufacture in which the copper content is first precipitated as a copper sulphide, the improvement consisting in suspending the sulphide in an alkaline solution of a metallic base, and agitating that solution and permeating it with air during the agitation.

5. A process of recovering copper content from the precipitating liquor of the cupro-ammonium process of rayon manufacture which consists in first converting the copper content to a copper sulphide by adding an equivalent amount of a suitable sulphide and removing the resultant insoluble precipitate of copper sulphide by suitable means, suspending the copper sulphide in a solu tion of a fixed alkali, agitating the solution while permeating it with air and dissolving the resulting copper hydroxide in waste acid liquor of the same cupro-ammonium process which contains part of the original copper content in the form or" copper sulphate and a certain percentage of free acid, whereby the free acid is neutralized and the copper content more readily recovered from the solution.

6. A process of producing copper hydroxide from copper sulphide which consists in agitating while permeated with air a solution of the following proportions and general characterizations; 1,000 pounds of a press-cake containing about 190 pounds of precipitated copper sulphide and 3,000 liters of water, together with pounds of caustic soda 50 per cent; and continuing the agitation until the sample is completely soluble in acid.

7. A process of converting copper sulphide as derived from the alkaline precipitating liquor utilized in the production of rayon by the cuproammonium method which consists in agitating while permeated with air a solution of the following proportions and general characteristics; 4,000 liters of the withdrawn copper sulphide sediment of the precipitating liquor of rayon manufacture containing 275 pounds of copper sulphide and 121 pounds of caustic soda brought to an aggregate of 6,000 liters by adding water; the treatment being continued until a sample is substantially completely soluble in acid.

8. A process of recovering copper content from the precipitating liquor of the cupro-ammonium process of rayon manufacture which consists in first converting the copper content to a copper sulphide by adding an equivalent amount of a suitable sulphide and removing the resultant insoluble precipitate of copper sulphide by suitable means, suspending the copper sulphide in a solution of a fixed alkali, agitating the solution while permeating it with air and dissolving the resultant copper hydroxide in acid.

GEORGE T. 'I'RAUT. 

